The present invention relates generally to microwave transmissions and, more particularly, to providing microwave radiation and/or waveguide transmissions from a hermetically-sealed monolithic microwave integrated circuit (MMIC) subsystem assembly.
It has proven difficult to allow directed millimeter wave signal radiation from internal elements formed on the circuit side of a microstrip substrate through its top cover, bottom base or side walls of a hermetically-sealed MMIC subsystem assembly. This is because the subsystem assembly requires a hermetic seal, radio frequency grounding and radio frequency shielding to properly launch the millimeter wave signals.
Providing a waveguide launch from the bottom base of the hermetically-sealed subsystem assembly has previously been performed using a microstrip launch requiring a "dog house" type of cover formed over the radiating element or launch probe plus a narrow microstrip channel formed in the microstrip substrate to prevent waveguide mode leakage. The dog house cover is used to provide the required waveguide backshort termination and mode filter.
Other methods for transmitting the radiated energy have included the use of hermetic coaxial ports. For use in the millimeter waveband, however, hermetic coaxial ports must be very small and hence, the coaxial glass seals, which themselves are difficult to assemble and bond, must be soldered to the housing wall between the MMIC chips and a conventional coaxial-to-waveguide launch probe. This is a time consuming, labor intensive and costly process.
There is therefore needed a structure which allows radiating elements to be placed on the chip side of the microstrip substrate to radiate millimeter waves outward from the subsystem assembly while allowing maximum heat conduction from the chip to the housing base. The radiating elements or launch probes should be capable of radiating signals through the hermetically-sealed housing cover and side walls as well as through the housing base to a hermetically-sealed waveguide port coupled thereto.
The present invention provides a number of structures allowing directed millimeter wave radiation from internal elements of a microwave circuit through the housing cover, housing base, and side walls of a hermetically-sealed MMIC integrated subsystem assembly. A "waffle-wall" configured array of conductive posts are provided between the assembly's housing cover and microstrip substrate to prevent X-Y direction waveguide propagation parallel to the microstrip substrate by providing an electrical connection from the microstrip substate's ground plane up to a metallic top shield of the cover. This two-dimensional periodic post structure functions as a band rejection filter to provide the "walls" which guide the radiated waves through a hermetically sealed window in the housing base for waveguide propagation or to a dielectric side wall or cover to radiate energy therethrough. The periodic array of conductive posts are configured in the waffle-wall pattern as described in copending application Ser. No. 591,034, now U.S. Pat. No. 5,065,123 filed on an even date herewith and assigned to the Assignee of the present invention, the specification of which is herein incorporated by reference.
The present invention provides a waveguide launch from a typical E field launching probe to a hermetically-sealed waveguide port coupled through the housing base of the integrated subsystem assembly. The launch probe is printed on a TEM mode microstrip transmission line substrate and is located over or on a glass or ceramic dielectric window formed at the end of an air filled waveguide, e.g. a circular or rectangular waveguide. A waveguide-like mode of propagation is launched perpendicular to the microstrip substrate and the energy is transmitted through the dielectric window into the air dielectric waveguide which extends through the housing base.
The present invention further allows radiating elements to be placed near the side walls of the subsystem assembly for use as sidewall-mounted antennas. The sidewall-mounted antenna has a typical vertical E field radiating element or launch probe located near the ceramic dielectric side wall and surrounded on its remaining three sides by the conductive posts of the waffle-wall configuration. The vertical E field launch probe is bonded to the end of a microstrip transmission line on the microstrip substrate. The launch probe launches a vertically polarized TE-type waveguide mode between the microstrip substrate's ground plane and the parallel conducting surface of the housing cover. The launched wave propagates toward the dielectric side wall to radiate outwardly from the subsystem assembly. The waffle-wall configuration of conducting posts prevents any wave propagation over the microstrip substrate by functioning as a band rejection filter in all directions (except toward the side wall) parallel to the ground plane.
Similarly, for radiating energy through the subsystem assembly cover, a launch probe is located under a dielectric aperture in the hermetically-sealed cover. A waveguide-like mode of propagation is launched perpendicular to the microstrip substrate and exits through the dielectric aperture located directly above. Again, the waffle-wall conductive post structure provides the necessary waveguide mode ground current connection from the ground plane up to the cover's conducting surface.
It is an advantage of the present invention to provide a waveguide launch from a housing base having lower attenuation and higher phase repeatability than the previously mentioned glass-sealed coaxial launches.
The edge o side wall radiating elements provide the capability of designing miniature millimeter wave MMIC integrated receiver/transmitter subsystem assemblies having the capability to switch or compare sector beams over a 360.degree. azimuth. When combined with the cover radiating elements, full hemisphere coverage is obtained. The present invention can be used for direction finding, radar warning receivers, directional communications, aircraft-carrier-to-aircraft initialization data links, satellite-to-satellite communications links, tank-to-tank communications, etc.
It is a further advantage of the present invention to provide radiating elements and waveguide launches which are of lower cost, size, and weight than current designs. Further, the waffle-wall configuration provides flexibility for many miniature millimeter wave communications applications.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.